How to print out the line after the line found in re.compile()

Question

Using this code

import re
file = open('FilePath/OUTPUT.01')
lines = file.read()
file.close()
for match in re.finditer(r"(?m)^\s*-+\s+\S+\s+(\S+)", lines):
eng = match.group(1)
open('Tmp.txt', 'w').writelines(eng)
print match.group(1)

I get a column of data that looks like this:

-1.1266E+05
-1.1265E+05
-1.1265E+05
-1.1265E+05
-1.1264E+05
-1.1264E+05
-1.1264E+05
-1.1263E+05
step
-1.1263E+05
-1.1262E+05
-1.1262E+05
-1.1261E+05
-1.1261E+05
-1.1260E+05
-1.1260E+05
-1.1259E+05
step
-1.1259E+05
-1.1258E+05
-1.1258E+05
-1.1258E+05
-1.1257E+05
terminating.
eng_tot
-1.1274E+05
3D

How do I write it a file (Tmp.txt)? As of now it only writes the last line '3D'. Also I'd like to eliminate all the lines that aren't of the form x.xxxxExxx (i.e. just the numbers).

Answer 1

i is the index into lines that line is at, so i+1 is the next line:

print lines[i+1]

Make sure the ---- isn't the last line or this will try to read from a location that doesn't exist. Also, your regular expression \s+-+\s+ requires that there be spaces before and after the -s, as \s+ means 1 or more spaces; you probably meant \s*

Answer 2

You could use a single regex:

file = open('FilePath/OUTPUT.01')
lines = file.read()
file.close()
with open("output.txt","w") as f:
    for match in re.finditer(r"(?m)^\s*-+\s+\S+\s+(-?[\d.]+E[+-]\d+)", lines):
        f.write(match.group(1)+"\n")

This should write all the second numbers that occur after a line that consists entirely of - into the file output.txt.

This regex assumes that the columns are space-separated, and that the first column will never be empty.

Explanation:

(?m)                 # allow ^ to match at start of line, not just start of string
^                    # anchor the search at the start of the line
\s*                  # match any leading whitespace
-+                   # match one or more dashes
\s+                  # match trailing whitespace, including linebreak characters
\S+                  # match a run of non-whitespace characters (we're now one line ahead of the dashes
\s+                  # match a run of whitespace
(-?[\d.]+E[+-]\d+)   # match a number in scientific notation

Answer 3

I wouldn't bother with REs for this. Try the following:

output = file("tmp.txt", "w")        # open a file for writing
flagged = False                      # when 'flagged == True' we will print the line
for line in file("FilePath/OUTPUT.01"):
    if flagged:
        try:
            result = line.split()[1] # python is zero-indexed!
            print>>output, result    # print to output only if the split worked
        except IndexError:           # otherwise do nothing
            pass
        flagged = False              # but reset the flag
    else:
        if set(line.strip()) == set(["-"]): # does the line consist only of '-'?
            flagged = True           # if so, set the flag to print the next line

Here's a version which allows you to specify the number of lines offset, and the column number:

OFFSET = 3 # the third line after the `----`
COLUMN = 2 # column index 2

output = file("tmp.txt", "w")
counter = 0                           # 0 evaluates as False
for line in file("FilePath/OUTPUT.01"):
    if counter:                       # any non-zero value evaluates as True
        if counter == OFFSET:
            try:
                result = line.split()[COLUMN] 
                print>>output, result # print to output only if the split worked
            except IndexError:        # otherwise do nothing
                pass
            counter = 0               # reset the flag once you've reached the OFFSET line
        else:
            counter += 1
    else:
        if set(line.strip()) == set(["-"]): # does the line consist only of '-'?
            counter = 1